Traditionally intravenous infusion has been accomplished using gravity flow systems or drip regulated systems. Modern advances for regulating intravenous infusion have included various types of volumetric pumping systems. In situations where a patient is already established with a gravity-fed or drip-type IV, it often becomes helpful to convert the same system into one with a pump-controlled volumetric flow. For example, an emergency IV can be established in the field by paramedics, and upon arrival at a hospital, a doctor may need to administer medication at a precisely controlled flow rate. The same IV tubing system can then be conveniently adapted for controlled volumetric flow pumping through the use of various types of peristaltic pumps which engage the exterior of the established IV tubing. The typical IV tubing is made of a medical grade polyvinyl chloride (PVC) which has thin walls and is both flexible and resilient. Other more expensive tubing has been proposed to reduce collapsing, but at a cost of about ten times as much as PVC tubing. Alternatively, a combination of types of tubing has been proposed, such as silicon tubing spliced along a length which will be subjected to peristaltic pumping action. Such combination systems can also have a cost significantly greater than PVC (about five to eight times as much), because of the materials, splicing and additional sterilization required. Pumps which act upon the outside of the tubing walls to pump fluid within the tubing at a controlled rate permit the medical practitioners to avoid disturbing existing catheters or needles already established into the patient.
Thus, various types of modern pumps have been used for pumping fluid through an IV tubing, including pumps with a rotating arm, with rollers affixed at both ends of the arm. The rollers are positioned adjacent a curved IV holding channel to engage and roll along a section of tubing placed into the holding channel, thereby advancing a column of liquid therethrough. As the arm rotates, the rollers alternately engage the tubing, one behind the other, and successive columns of liquid are moved through the tubing. Rotation of the arm continues and repeats the pumping action.
Another type of pump is one which is referred to as a single-plunger peristaltic pump. This type of pump has an entry valve which compresses the tubing shut at an upstream point. A single elongated plunger then squeezes a predetermined length of the tubing along a linear section ahead of the closed entry valve. An outlet valve then compresses the tubing downstream from the elongated plunger after the liquid in the linear section is squeezed out and moved toward the patient. With the outlet valve closed, the entry valve is opened and the elongated plunger is retracted to allow fluid to move back into the linear section between the entry valve and the outlet valve. The entry valve is then closed, and the outlet valve is opened so that compression of the single elongated plunger can pump more fluid through the tubing.
Another type of pump, which is referred to here as a linear peristaltic pump, uses a series of pumping elements which each engage and sequentially compress a plurality of small segments along an engaged portion of the IV tubing. Each pumping element in sequence at its maximum stroke acts as a seal valve to prevent unwanted reverse flow. Separate inlet and outlet valves are not required in such a linear peristaltic pump. The sequence repeats, and the pumping element reciprocating strokes are typically timed to repeat the milking cycle without interruption. The rate of flow is controlled by changing the rate of reciprocation while the magnitude of the stroke is constant.
With each of the various types of peristaltic pumps described above, the IV tubing is repeatedly collapsed to force the fluid out of the tubing in one direction and then released to allow fluid to reenter from the other direction. After a period of use, the PVC tubing material becomes progressively flattened and permanently deformed such that the walls become creased and the interior volume of the tubing changes over the normal time period of operation. Tubing subject to permanent deformation reduces the pumping efficiency and reduces the accuracy of the pump. To the extent that attempts at reshaping may cause additional crease lines, the risk of premature cracking, tearing or rupture may also be increased, particularly at crease lines. Thus, the tubing must be changed frequently and must be carefully monitored to avoid lost efficiency, inadequate flow, inaccurate and improper volumetric flow or other failure of the system.